Respiratory diseases including cystic fibrosis, asthma, chronic obstructive pulmonary disease, bronchitis, and other respiratory diseases characterised by an inflammatory response are particular difficult diseases to diagnose early and/or monitor during therapy.
The acoustic impedance of a human respiratory system is often measured to obtain information concerning resistive and elastic properties of airways and tissues. Emphysema, for example, affects the elastic properties of the airways and tissues and it is possible to diagnose emphysema from results of the acoustic impedance measurements.
Acoustic impedance measurements of the human respiratory system are usually conducted using a forced oscillation technique in which acoustic waves are directed into the respiratory system and a response is detected. Frequencies that are selected for the acoustic waves are relatively low, such as a few Hertz, as for such low frequencies mathematical models are available that facilitate analysis of the measurement data. A patient breathes during the acoustic impedance measurements and the obtained data are characteristic for one or more breathing cycles.
Such measurements are useful as they provide valuable information about the respiratory system. For a more comprehensive diagnose, however, additional information is required and there is a need for technological advancement.